With an increasing demand for communication, high-speed optical transmission methods have been standardized. For example, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) recommendation G.709 prescribes the technique of the optical transport network (OTN) of about 2.5 to 100 Gbps.
The OTN enables large-capacity optical transmission by multiplexing a plurality of optical signals each accommodating a user signal according to the wavelength division multiplexing (WDM) technique. Examples of the user signal accommodated in the optical signal include a synchronous digital hierarchy (SDH) frame, a synchronous optical network (SONET) frame, and an Ethernet (trademark) frame.
In accommodation design processing targeted for such network, it has been expected to cut costs of the entire network by optimizing an upper order layer to a lower-order layer in an integrated manner. Because of the progress of standardization, in the layer handing packets as well as the lower-order layer such as the OTN, the protection band using shared protection is progressing.
For example, in the OTN, signaling and shared protection that use generalized multi-protocol label switching (GMPLS) in the internet engineering task force (IETF) Internet Draft draft-ietf-ccamp-gmpls-signaling-g709v3 have been examined. The shared protection enables sharing a protection network resource between working traffics that do not share a fault scenario.
Concerning network design, Japanese Laid-open Patent Publication No. 04-263540 describes that a predetermined number of lines are previously assigned to a protection link, and some of the assigned lines are deleted so as to satisfy the fault repair rate. Japanese Laid-open Patent Publication No. 2003-115872 discloses a method of achieving band sharing of a protection path. Japanese Patent No. 5151387 describes that protection is applied to an upper order layer in a multi-layer network based on the protection type supplied from the lower-order layer.
In the network to which shared protection is applied can share the band with a plurality of protection paths to provide protection with reduced network resource. In the multi-layer environment, it is desirable to apply shared protection to a lowest possible layer. The reason is that the granularity of traffics in the lower-order layer is large, increasing the reduced amount of the network resource (reduced amount of the band) by sharing the protection band. In addition, the reduction of the band in the lower-order layer tends to directly lead to reduction of a physical interface, largely reducing equipment costs.
Therefore, in the multi-layer network, it is desirable to transfer the layer to which shared protection is applied to the lowest possible layer. According to the normal multi-layer design method, optimum design is generally made for each layer, but in some cases, protection is not transferred to the lower-order layer.